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Ok, now I'm really confused. Can I install a double check valve backflow prevention device; being the "Greenhorn" that I am, or do I need to have an assortment of inspection devices?

You do not have to purchase the inspection devices. But depending upon local codes, you may have to pay a certified plumber to inspect/test your backflow.

As a mater of fact, if you have not yet, the 1st thing you need to do is check with local building code. Legal requirements range from "do what ever you want... you are liable for your own actions" to "only a certified plumber is allowed to install irrigation".

Typical legal requirements are usually one of the following:

You must install a backflow preventer (no legal requirements as to which , to test, or inspect).
You must install one of these backflow preventers ___, ____, ____
(the list can be as short as specifying a particular part number)
You must install a backflow preventer and have it tested by a certified plumber annually.
A certified plumber is required to install all irrigation lines from the mainline to the backflow preventer.

The test equipment is a differential pressure gauge. Mine is a 5 needle gauge that was 750.00. The class to inspect backflow devices was 550.00. It was a 1 week long class with no phone access and getting wet in the field (priceless).

Test Equipment??

Generally speaking, double checks can be installed in any orientation because they don't rely on gravity and they don't discharge water.

There does need to be enough clearance around the device such that testing equipment can be properly connected to test cocks.

Double Checks have no fail-safe, therefore they are not suitable in situations where contaminates are known to be present. You can think of it this way... a double check can easily fail. All it takes is some trash in the lines that gets wedged in the check valve and prevents it from sealing. And if trash has fouled on of the check valves, it likely will fail both. Now in the case of just regular irrigation, there is so little chance of contaminants making their way from the lawn all the way back to the water supply, that you can risk having a device that might fail. But in the case of injecting contaminates into the system, the risk of those contaminates making it back into the water supply is high, so you must have a fail-safe device. This basically requires an RPZ (because it's designed such that when it fails to work properly, it dumps water out rather than allowing it to back flow). Even a PBV is not suitable when injecting something into the water because the "magic" of the PBV is that it's designed to prevent backflow caused by gravity alone. With the device located higher than the sprinkler heads, so there is no way the water acting on gravity alone could flow back through the device. But if you are injecting something into the water, then there exists the potential for water to be forced backward through the device.